177. Inspected by the naked eye alone, the stakes 10 and 11, where the glacier reaches its greatest motion, are seen to be considerably to the west of the axis of the glacier. Thus far we have a perfect verification of the _guess_ which prompted us to make these measurements. You will here observe that the "guesses" of science are not the work of chance, but of thoughtful pondering over antecedent facts. The guess is the "induction" facts, to be ratified or exploded by the test of subsequent experiment. 178. And though even now we have exceedingly strong reason for holding that the point of maximum velocity obeys the law of liquid motion, the strength of our conclusion will be doubled if we can show that the point shifts back to the eastern side of the axis at another place of flexure. Fortunately such a place exists opposite Trélaporte. Here the convex curvature of the valley turns again to the east. Across this portion of the glacier a line was set out on July 28, and from measurements on the 31st, the rate of motion per 24 hours was determined. Fifth Line: E E' upon the Sketch. West East Stake 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Inches 11 14 13 15 15 16 17 19 20 19 20 18 16 15 10 179. Here, again, the mere estimate of distances by the eye would show us that the three stakes which moved fastest, viz. the 9th, 10th, and 11th, were all to the east of the middle line of the glacier. The demonstration that the point of swiftest motion wanders to and fro across the axis, as the flexure of the valley changes, is, therefore,--shall I say complete? 180. Not yet. For if surer means are open to us we must not rest content with estimates by the eye. We have with us a surveying chain: let us shake it out and measure these lines, noting the distance of every stake from the side of the glacier. This is no easy work among the crevasses, but I confide it confidently to Mr. Hirst and you. We can afterwards compare a number of stakes on the eastern side with the same number of stakes taken at the same distances from the western side. For example, a pair of stakes, one ten yards from the eastern side and the other ten yards from the western side; another pair, one fifty yards from the eastern side and the other fifty yards from the western side, and so on, can be compared together. For the sake of easy reference, let us call the points thus compared in pairs, _equivalent points_. 181. There were five pairs of such points upon our fourth line, D D', and here are their velocities: Eastern points; motion in inches 13 15 16 18 20 Western " " " " 15 17 22 23 23 In every case here the stake at the western side moved more rapidly than the equivalent stake at the eastern side. 182. Applying the same analysis to our fifth line, E E', we have the following series of velocities of three pairs of equivalent points:--